What is Humus?

The need for constantly replacing organic matter in soil lies in its vital role in building up the humus content. But what is humus? Actually, nobody really knows. It is somehow tied up with lignin (a substance from wood), with protein and a colloidal complex – that about states what we know about it. The three or four lignin chemists who know more about it than anyone else differ and argue about its composition.

But what humus does is far from mysterious. It is so thirsty that it will absorb between 80% and 90% of the water in a saturated atmosphere. In comparison, the best clay can do is to absorb 20%. It makes soil nutrients much more available. It breaks down slowly, releasing its protein in the form of nitrogen over a period of from five fifty years. Thus it is a “built-in” source of plant nutrients available even when other sources fail.

An important function of humus is to pull tiny soil particles such as clay into clumps or “crumbs,” which make a heavy clay more porous, easier to work, and a better place in which to grow plants.

The breakdown of organic matter into humus is slower when fats and waxes are present, but the final release of the desirable elements in humus is correspondingly slowed up. Because of the more rapid destruction of humus in tropical and subtropical climates, it has little chance to accumulate. This means that organic matter is used up faster in such climates and must be replaced more often. Humus in warm climates is lighter in color; in northern soils it is often a deep blackish brown.

Humus in Soil

What is humus? For practical purposes, humus may be defined as the resultant brown or dark brown substance that develops following the breakdown of organic materials by various soil organisms. Actually, no one knows the exact chemical composition but a soil gel with lignin, a component, is as good a definition as any.

How does one recognize the different types of humus, such as peat, leaf mold, muck, etc? Peat: soft, brown, spongy, semi-granular material; domestic peats, unless kiln dried, contain more water than the imported type. Muck: black, represents further state of decay than peat – not so useful. Bacterized Peat: supposedly treated; usually no better than muck. Leaf mold: brownish black material with some undecomposed leaves and twigs present; useful soil conditioner. Wood Soil: usually leaf mold, but further decomposed; useless without additions of fertilizer.

In what forms is potential humus available to the average home gardener? See previous question. Manure, straw, peat moss, kitchen waste, seaweed, sawdust, decayed wood chips, pine needles, hay – all these must decompose before becoming humus. The compost pile is probably the best of all sources of humus for the home garden.

What is the function of humus in the soil? Among the important functions of humus are to effect granulation of the soil, thereby improving drainage and soil aeration; to increase its water holding capacity; to increase the bacterial activity; to increase the percentage of such essential elements as nitrogen and sulfur; and to help in transforming essential elements from non-available to available forms.

Is humus important to soil fertility? Yes; by increasing moisture absorption and the activity of several of the essential elements, especially nitrogen.

How is humus incorporated into the soil? By spading or plowing.

Is spring or fall the best time to add humus to soil? Any time the soil can be worked. Humus does not injure growing plants.

Our soil is rich but hard to work. What is the best source of humus? Manure, peat moss, or a compost heap.

What method do you recommend to maintain humus and bacteria in soils? Keep soils aerated by the addition of compost and/or peat moss. Use green manure crops wherever possible.

What is to be done when humus keeps the earth too moist? Incorporate sand or weathered steam cinders.

What would you recommend to keep a very rich black soil from caking? It forms a hard crust about an inch deep. Add humus – manure, peat, alfalfa hay. Incorporate fine steam cinders in the top 6 ins.

What causes soil to become very hard? Lack of organic matter.

A bog was dug up to make a lake; stuff removed looks like excellent humus. How can this material be converted to garden use? The material should make an excellent mulch, or to mix with soil. Unless soil on which this is used is very acidic, the acidity of the humus will have no detrimental effect. If the material is lump, place in small piles to dry; pulverize before applying.

Do commercial fertilizers supply humus? The application of organic fertilizers such as soybean and cottonseed meals supplies a very small amount of humus. The inorganic fertilizers do not supply humus.